1. Field of the Invention
The present invention relates to a control device and a control method for an internal combustion engine with a supercharger which can estimate an upstream pressure of a throttle valve (hereinafter, occasionally referred to simply as throttle upstream pressure) in a supercharging path extending from a compressor of a supercharger to the throttle valve, provided in an intake (i.e. suction or inlet) system of an internal combustion engine.
2. Description of the Related Art
Control systems for engines with superchargers for the purpose of enhancing the output of an internal combustion engine (hereinafter, occasionally abbreviated as engine) are conventionally known. As examples of “supercharger”, turbochargers in which a turbine is rotated at high speed by the energy of an exhaust gas to thereby drive a compressor mounted on an intake system of engine, and mechanical superchargers in which a compressor is mounted on an intake system of engine and driven through a belt or the like from a crank shaft, and the like are known.
As a system or method for detecting an amount (i.e. quantity) of intake air in an engine control system, there have been known a system for detecting same with an air flow sensor (hereinafter, occasionally abbreviated as AFS), and a so-called speed density system which estimates same based on a pressure within an intake manifold.
In the former AFS system, an air flow (i.e. air flow rate) passing through a portion on which an AFS is mounted (hereinafter, occasionally referred to as AFS intake air amount) is directly measured and air flow flowing into a cylinder (hereinafter, occasionally referred to as cylinder intake air amount) in a normal operation is approximately equal to the AFS intake air amount, so that the AFS system has the feature that the calculation error of the cylinder intake air amount during normal operation is relatively small compared with the speed density system.
Adjustment of engine output is generally carried out by operating a throttle valve (hereinafter, occasionally referred to simply as a throttle or THV) provided in an air intake path and by adjusting the opening area of the air intake path. It is possible to control the air passing through the throttle valve based on a physical calculating equation with detected values of the opening area of the throttle valve, pressure upstream/downstream of the throttle valve related to the flow of air, temperature upstream/downstream of the throttle valve, and the like. This technology is generally used as described in Japanese Patent No. 4,237,214, for example.
However, such a technology is disadvantageous in that a sensor for measuring the pressure upstream of the throttle valve must be provided, thereby increasing the number of parts and cost.
On the other hand, there is a technology for estimating throttle upstream pressure based on intake manifold pressure and average atmospheric density, in which average atmospheric density of a region having combined a turbocharging path extending from the compressor of the turbocharger to the throttle valve with the intake manifold portion is calculated based on AFS intake air amount and cylinder intake air amount.